This invention relates to a dry analytical element capable of analyzing whole blood sample.
Recently, biochemical assay of blood has been frequently conducted, and dry analytical elements tend to be used for the biochemical assay.
In the past, the sample to be analyzed was usually blood serum or blood plasma where the erythrocytes were removed, irrespective of whether the wet or dry method was used. However, since the separation of erythrocytes requires labor and equipment cost, analysis is preferably carried out using undiluted whole blood.
When whole blood is analyzed by the dry method, blood cells, i.e. erythrocytes and leukocytes, and other solid components should be separated in the analytical element by some means. A means therefor is to provide a blood cell-separating layer in a multilayer anlaytical element. Japanese Patent KOKAI Nos. 57-53661 and 61-96466 disclose that glass fiber, membrane filter, cottom fiber, wool fiber and the like can be used for the blood cell-separating layer. It is also known to combine two or more layers, and Japanese Patent KOKAI Nos. 62-138756 and 3-16651 disclose to combine a fibrous porous layer and a nonfibrous porous layer.
The blood cell components of whole blood is great ranging over 70% as hematocrit value. Accordingly, permeation and diffusion of plasma portion were liable to be uneven due to the occurrence of clogging in the blood cell-separating layer. As a result, there was a problem that analytical results varied according to the measured portion in the analytical element resulting to induced errors. Besides, it was also a great problem that the analytical errors caused by scattering of the spotted amounts of whole blood sample and scattering of hematocrit values. Moreover, since whole blood samples have a high viscosity, it is difficult to take a very small amount and to spot it accurately. Therefore, it is very difficult to put a simple blood analytical element to practical use without a means to decrease the above liquid amount errors.